The present disclosure relates to a successive approximation analog-to-digital (A/D) converter configured to convert an analog signal, which is externally input, into a digital signal, an imaging device, an endoscope, and a setting method.
As a low power consumption analog-to-digital (A/D) converter, a differential input asynchronous successive approximation A/D converter has been known (for example, in “A 26 μW 8 bit 10 MS/s Asynchronous SAR ADC for Low Energy Radios”, IEEE JOURNAL OF SOLID-STATE CIRCUITS, Vol. 46, No. 7, pp. 1585-1596, July 2011). This successive approximation A/D converter holds a pair of analog signals input in a sample hold circuit as a differential input signal, and causes comparison circuit to generate a comparison voltage signal by reflecting a reference signal in the held analog signals through a capacitor circuit. Based on this comparison voltage signal, a successive-approximation logical circuit determines respective bit values (0 or 1) of MSB to LSB of the digital signal corresponding to the differential input signal according to a binary search algorithm, and feeds back the determined respective bit values to the reference signal.
The successive approximation A/D converter can be configured mostly with a digital circuit, without using an analog circuit, such as an operational amplifier. Therefore, the successive approximation A/D converter can be implemented in a small size by using a minute complementary metal oxide semiconductor (CMOS) process, and can reduce power consumption. In terms of capability of reducing power consumption and downsizing, the successive approximation A/D converter is used for a system large scale integration (LSI) of, for example, a mobile device.